Daylight saving time
What is daylight saving time?
Daylight saving time moves clocks forward, usually by one hour, for part of the year. This puts sunset later on the clock without changing the amount of daylight. Some places use it and others do not.
The sky does not change
On the spring-forward night, 2:00 a.m. becomes 3:00 a.m. You lose an hour of sleep. The Sun still rises when the Earth has turned far enough. Only the number on the clock jumped.
Arizona (mostly) and Hawaii do not do this. Most of Europe does. That is why a world clock has to know the rules, not just a fixed offset.
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Why the clock, not the Sun
The original pitch was to move an hour of daylight from the morning, when fewer people are out, to the evening. Whether it saves energy is argued. What it definitely does is change every offset from UTC for a few months, which is why a sunrise table that ignored DST would be an hour wrong all summer.